As the information industry develops, processing a large amount of information is required and, thus, the demand for high-capacity information storage media is continuously increasing. As the demand for the high-capacity information storage media increases, research into small-sized information storage media having high data storing speed have been conducted, and, as result, various types of conventional information storage devices have been developed.
Conventional information storage devices can largely be classified into volatile information storage devices and non-volatile information storage devices. In the volatile information storage devices, stored information is erased when power is turned off. However, the volatile information storage devices may write and read information at high speeds. In the non-volatile information storage devices, stored information is not erased when power is turned off.
A volatile information storage device may be a dynamic random access memory (DRAM). A hard disk drive (HDD) and a non-volatile random access memory (RAM) are non-volatile data storage devices. A magnetic random access memory (MRAM), which is a non-volatile information storage device, may use a magnetoresistance effect based on a spin dependent electron transport phenomenon.
Conventional MRAM devices may include a magnetoresistance structure and a switch structure which are connected to each other. The magnetoresistance structure may include an antiferro-magnetic layer, a pinned layer, a non-magnetic layer, and a free layer, and the switch structure may be a transistor.
MRAM devices may use a spin transfer torque (STT) phenomenon to address the problem of high writing current, and improve integrity and selectivity. In STT, a free layer of the MRAM device may be switched to a desired direction using a spin transfer of electrons by allowing a current in which spins are polarized to flow in the MRAM device. Densification may be realized since the required current is decreased as the cell size is reduced.
However, a critical current density required for switching the MRAM devices that use the STT phenomenon is too large for the magnetic memory devices to be commercialized. If a free layer of a magnetoresistance structure is magnetized in a direction different from that of a pinned layer, resistance is too large. If the free layer is magnetized in a same direction as that of the pinned layer, resistance is too small. Since the resistance may greatly vary depending on the direction of the magnetic filed, current flowing in the magnetoresistance structure may become asymmetric.
A conventional MRAM device may have a transistor structure including a source, a drain, and a gate electrode, and a magnetoresistance structure connected to the source or the drain. The magnetoresistance structure may be connected to a bit line, and the gate electrode may be connected to a word line.
In a process of writing information to a conventional MRAM device, a voltage VDD is applied via a word line regardless of the data to be stored. Accordingly, a source voltage Vs may be changed due to the direction the magnetoresistance structure is magnetized. Consequently, a current value IDS between the source and the drain flowing in a first direction may be different from the current value IDS flowing in a second direction between the source and the drain.
As a result, the amount of current +I and −I flowing through the magnetoresistance structure becomes asymmetric due to the difference of the current value IDS between the source and the drain. Therefore, a tunneling barrier layer of the magnetoresistance structure M may break, or current required to perform a writing operation may not be secured.